Method for aligning high density infrared detector arrays

ABSTRACT

A method for aligning infrared detector arrays having a high density of pixel elements to the surface of a signal processing module or the like is disclosed. The process comprises the steps of forming a plurality of indicia upon the second side of the infrared detector array, forming a corresponding plurality of reference indices upon the support surface, the indices being disposed in a predetermined position relative to the electrical connectors, attaching the second side of the infrared detector array to a transparent substrate and positioning the detector array adjacent the support surface and aligning the indicia to the reference indices by observing the indicia formed upon the second side of the array by looking through the transparent substrate. Three embodiments of indicia are disclosed. A through hole indicia passes from the first surface of the infrared detector array to the second surface thereof, a plurality of fiducial indicia can be formed upon the second surface of the infrared detector array, or notches can be formed in the edges of the infrared detector array and/or substrate.

FIELD OF THE INVENTION

The present invention relates generally to infrared detector arrays andmore particularly to a method for aligning infrared detector arrayshaving a high density of pixel elements to the surface of a signalprocessing module or the like.

BACKGROUND OF THE INVENTION

The infrared spectrum covers a range of wavelengths longer than thevisible wavelengths but shorter than microwave wavelengths. Visiblewavelengths are generally regarded as between 0.4 and 0.75 micrometers.Infrared wavelengths extend from 0.75 micrometers to 1 millimeter. Thefunction of an infrared detector is to respond to energy of a wavelengthwithin some particular portion of the infrared region.

Heated objects will dissipate thermal energy having characteristicwavelengths within the infrared spectrum Different levels of thermalenergy, corresponding to different sources of heat, are characterized bythe emission of signals within different portions of the infraredfrequency spectrum. No single detector is uniformly efficient over theentire infrared frequency spectrum. Thus, detectors are selected inaccordance with their sensitivity in the range corresponding to theparticular detection function of interest to the designer. Similarly,electronic circuitry that receives and processes the signals from theinfrared detector must also be selected in view of the intendeddetection function.

A variety of different types of infrared detectors have been proposed inthe art since the first crude infrared detector was constructed in theearly 1800's. Virtually all contemporary infrared detectors are solidstate devices constructed of materials that respond to infrared energyin one of several ways. Thermal detectors respond to infrared energy byabsorbing that energy and thus causing an increase in temperature of thedetecting material. The increased temperature in turn causes some otherproperty of the material, such as resistively, to change. By measuringthis change the infrared radiation can be derived.

Photo-type detectors (e.g., photoconductive and photovoltaic detectors),absorb the infrared frequency energy directly into the electronicstructure of the material, inducing an electronic transition which leadsto a change in the electrical conductivity (photoconductors) or to thegeneration of an output voltage across the terminals of the detector(photovoltaic detectors). The precise change that is affected is afunction of various factors including the particular detector materialselected, the doping density of that material and the detector area.

By the late 1800's, infrared detectors had been developed that coulddetect the heat from an animal at one quarter of a mile. Theintroduction of focusing lenses constructed of materials transparent toinfrared frequency energy, advances in semiconductor materials and thedevelopment of highly sensitive electronic circuitry have advanced theperformance of contemporary infrared detectors close to the ideal photonlimit.

Current infrared detection systems incorporate arrays of large numbersof discrete, highly sensitive detector elements, the outputs of whichare connected to sophisticated processing circuitry. By rapidlyanalyzing the pattern and sequence of detector element excitation, theprocessing circuitry can identify and monitor sources of infraredradiation.

Though the theoretical performance of such systems is satisfactory formany applications, it is difficult to actually construct structures thatmate a million or more detector elements and associated circuitry in areliable and practical manner. Consequently, practical applications forcontemporary infrared detection systems have necessitated that furtheradvances be made in areas such as miniaturization of the detector arrayand accompanying circuitry, minimization of noise intermixed with theelectrical signal generated by the detector elements, and improvementsin the reliability and economical production of the detector array andaccompanying circuitry.

A contemporary subarray of detectors may, for example, contain 256detectors on a side, or a total of 65,536 detectors, the size of eachsquare detector being approximately 0.0035 inches on the side with0.0005 inches spacing between detectors. Such a subarray would thereforebe 1.024 inches on a side. Thus, interconnection of such a subarray toprocessing circuitry requires a connective module with sufficientcircuitry to connect each of the 65,536 detectors to processingcircuitry within a square, a little more than one inch on a side. Thesubarray may, in turn, be joined to form an on-focal plane array thatconnects to 25 million detectors or more. Considerable difficulties arepresented in aligning the detector elements with conductors on theconnecting module and in isolating adjacent conductors in such a denseenvironment.

The outputs of the detectors must undergo a series of processing stepsin order to permit derivation of the desired information. The morefundamental processing steps include preamplification, tuned bandpassfiltering, clutter and background rejection, multiplexing and fixednoise pattern suppression. By providing a signal processing module thatperforms at least a portion of the processing functions within themodule, i.e. on integrated circuit chips disposed adjacent the detectorfocal plane, the signal from each detector need be transmitted only ashort distance before processing. As a consequence of such on focalplane or up front signal processing, reductions in size, power and costof the main processor may be achieved. Moreover, up front signalprocessing helps alleviate performance, reliability and economicproblems associated with the construction of millions of closely spacedconductors connecting each detector element to the main signalprocessing network.

Infrared detectors are typically fabricated from monolithicsemiconductor wafers by photolithographic techniques. The processedwafers are diced to form smaller arrays having various pixel sizes, suchas 32×32 or 8×128. A plurality of diced arrays are attached to thesignal processing modules. Many signal processing modules can beassembled to form a focal plane array.

Backside-illuminated detectors are well known. Backside-illuminateddetectors have an electrical contact fabricated upon the front side,thus necessitating illumination through the substrate. The focal planearray may be formed by attaching the diced arrays to signal processingmodules by flip-chip bump bonding.

In flip-chip bump bonding, the electrical contacts formed upon the frontsurface of the array are comprised of a soft, malleable conductivematerial such as indium. The indium bump bonds are electricallyconnected to corresponding contacts formed upon the signal processingmodule by flipping or inverting the infrared detector array such thatthe indium bump bonds contact the corresponding electrical contacts ofthe signal processing module. An epoxy filler may be used to secure theinfrared detector arrays upon the signal processing module.

Because of the brittle nature of the infrared detector array, a thinsubstrate material, such as cadmium telluride (CdTe) or sapphire istypically attached to the back side of the infrared detector array priorto flip-chip bump bonding. The substrate provides mechanical support tothe array and thereby facilitates handling.

A particular problem with the attachment of detector arrays to surfacessuch as the contacts of the signal processing module is alignment. Theback side or illuminated surface of the CdTe or sapphire substrate ispolished to provide a smooth surface. The smooth surface is required toprovide maximum absorption and transmission of incident infraredradiation to the detector elements. Therefore, no features exist uponthe back surface of the substrate to indicate the exact positions of thedetector element pixels of the infrared detector array beneath.

In the prior art, the detector pixel locations are determined bymeasuring the distance between the pixels and the array edges of thefront side. However, once an array is positioned for attachment to asignal processing module, only the back side is visible. Therefore, theedges of the back side must be used as an indirect reference. That is,since the front side edges of the infrared detector array to which theinitial measurement was made are not visible, the back side edges mustbe used instead. The rear edges of the diced array may not be true tothe front edges, e.g. due to tapers or chips in the substrate, thereforethe accuracy of using the back edges as references is quite limited.

The most accurate dicing equipment today has an average tolerance of ±5microns. In combining the errors due to imperfections on the edges withthe accuracy of dicing, an overall accuracy of using the back side edgesto locate the pixel is estimated to be approximately ±10 microns.

It is also necessary to know the precise locations of the pixel elementsof infrared detector arrays after they have been attached to signalprocessing modules. This is required when the signal processing modulesare being assembled into a staring focal plane array. The pixels must bealigned when the signal processing modules are formed into a focal planearray. Precise placement of the detector pixels is necessary to achievethe intended performance.

Placement of the pixels must be identifiable from the back side of thearrays both before and after they are attached to the signal processingelectronics in order to obtain the required performance. Therefore, itwould be desirable to provide a means for obtaining the preciselocations of the pixel elements formed upon the front side of thedetector array by visually observing the back side of the array.

SUMMARY OF THE INVENTION

The present invention specifically addresses and alleviates theabove-mentioned deficiencies associated in the prior art. Moreparticularly, the present invention comprises a method for aligninginfrared detector arrays having a high density of pixel elements formedupon its first surface to the surface of a signal processing module orthe like. The process comprises the steps of forming a plurality ofindicia upon the second side of the infrared detector array, forming acorresponding plurality of reference indices upon the support surface,the indices being disposed in predetermined positions relative to theelectrical connectors, attaching the second side of the infrareddetector array to a transparent substrate, positioning the detectorarray adjacent the support surface and aligning the indicia to thereference indices by observing the indicia formed upon the second sideof the array by looking through the transparent substrate.

Three embodiments of indicia are disclosed. A through hole indiciapasses from the first surface of the infrared detector array to thesecond surface thereof, a plurality of fiducial indicia can be formedupon the second surface of the infrared detector array, or notches canbe form®d in the edges of the infrared detector array and/or substrate.

In the first embodiment of the invention through holes are formed in theinfrared detector array by a process such as etching or laser drilling.Thus, the apertures extend through the detector array from the firstside to the second side thereof. The locations where the apertures areto be formed may be defined by providing corresponding indicia on adetector pixel implant mask such that the locations are marked with ahigh precision, on the first side of the array during the pixel implantprocess. An etchant specific to the detector material may be used suchthat the attached substrate is not etched.

In a second embodiment of the present invention indicia may be etchedupon the second side of the infrared detector array. The method forforming the indicia upon the second side of the infrared detector arraycomprises the steps of placing the detector array in a double sided maskaligner, aligning a mask for the second side of the detector array to aprimary reference located on the first side of the detector array, themask having indicia formed thereon, and exposing and developing thesecond side of the detector array to form the indicia upon the array.

In a third embodiment of the present invention a plurality of notchesare formed along at least one edge portion of the detector array. Thenotches extend substantially from the first side to the second side ofthe detector array, and may also extend across the substrate. Thenotches may be formed by disposing the detector array in a precisionlaser microprocessing machine and forming the notches with a laser. Alaser beam having a diameter of approximately 10 microns or less ispreferred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the front side of an infrared detectorarray according to a first embodiment of the present invention showingthe individual detector elements or pixels and also showing fourthrough-hole fiducial;

FIG. 2 is a perspective view of the front of the infrared detector arrayof FIG. 1 having a support substrate attached to the back side thereof;

FIG. 3 is a cross-sectional side view of a portion of the detector arrayof FIG. 2 showing a single through-hole fiducial and three detectorelement pixels;

FIG. 4 is a perspective view of the back side of the support substrateof FIGS. 2 and 3 depicting the four through-hole fiducial of theinfrared detector array visible therethrough;

FIG. 5 is a sectional perspective view of a signal processing moduleshowing the electrical contacts formed upon the connecting surfacethereof;

FIG. 6 is a perspective view of the signal processing module of FIG. 5showing an infrared detector array according to the first embodiment ofthe present invention attached thereto and another such infrareddetector array positioned to be attached thereto;

FIG. 7 is a top plan view of a circular fiducial according to a secondembodiment of the present invention;

FIG. 8 is a top plan view of a double square fiducial according to asecond embodiment of the present invention;

FIG. 9 is a perspective view of the back side of the support substratedepicting four double square fiducial formed upon the back side of theinfrared detector array according to the second embodiment of thepresent invention;

FIG. 10 is an enlarged perspective view of one double square fiducial ofFIG. 9;

FIG. 11 is a perspective view of the top and side surfaces of aninfrared detector array and support substrate having notches formed inthe edges thereof according to a third embodiment of the presentinvention; and

FIG. 12 is a perspective view of the front and top surfaces of threethin signal processing modules being stacked to form a mosaic focalplane array.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appendeddrawings is intended merely as a description of the presently preferredembodiments of the invention, and is not intended to represent the onlyform in which the present invention may be constructed or utilized. Thedescription sets forth the functions and sequence of steps forconstruction and implementation of the invention in connection with theillustrated embodiments. It is to be understood, however, that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

The method of aligning high density infrared detector arrays of thepresent invention is illustrated in FIGS. 1-12 which depict threepresently preferred embodiments of the invention.

Referring now to FIG. 1, an infrared detector array 10 has an 8×16 arrayof individual detector elements or pixels 12 formed upon the frontsurface 16 thereof. Each detector element or pixel 12 has an electricalcontact or bump 14 formed thereupon. Four through-hole fiducial 20 areformed in the infrared detector array 10. Each through-hole fiducial 20passes from the front or first 16 surface of the array 10 to the back orsecond 18 surface thereof. Thus, each through-hole fiducial 20 isvisible upon the back surface 18 of the array 10.

Referring now to FIG. 2, a support substrate 22 is attached in laminarjuxtaposition to the back side 18 of the infrared detector array 10.Infrared detector arrays are commonly comprised of a very thin andextremely brittle material such as mercury cadmium telluride, HgCdTe. Tofacilitate handling of the delicate infrared detector array 10 a supportsubstrate 22 comprised of an infrared transparent material such as CdTeor an optical and infrared transparent material such as sapphire isattached thereto. The thickness of the support substrate is typically onthe order of several hundred microns, thus providing substantialmechanical support to the infrared detector array and providing a meansof handling the delicate array 10.

The back side 26 of the support substrate 22 is polished to provide avery smooth surface. This is to facilitate the absorption andtransmission of infrared radiation from the back side of the substrate22 to the infrared detector elements 12. The smooth surface is requiredto reduce reflection and scattering of incident infrared radiation.Thus, no features exist upon the support substrate surface which can beused to indicate the positions of the infrared detector elements 12attached thereto.

The four through-hole fiducial 20 of the present invention thereforeprovide a means for visibly observing an indication of the positions ofthe infrared detector elements or pixels 12 from the back side 26 of thesupport substrate 22. That is, the fiducial 20 are observed by lookingthrough the substrate 22. This is possible because the support substrate22 is transparent to visible and/or infrared radiation. Thus, thefiducial 20 may be observed using a standard optical microscope or aninfrared camera. The fiducial 20 may therefore be used in the alignmentof the infrared detector array 10 to indices formed upon a signalprocessing module or the like.

Referring now to FIG. 3, a cross-sectional side view of the infrareddetector array 10 and support substrate 22 is depicted. Each fiducialthrough-hole 20 extends from the front surface 16 of the infrareddetector array 10 to the back surface 18 thereof. Thus, the through-holefiducial 20 are visible from the back side 26 of the transparent supportsubstrate 22.

Referring now to FIG. 4, the through-hole fiducial 20 are depicted asviewed through the transparent support substrate 22. Thus, a means isprovided for visually aligning the infrared detector elements 12 to aplanar surface such as a signal processing module. Alignment isperformed with respect to the through-hole fiducial 20 by visuallyobserving the through-hole fiducial 20 with a standard opticalmicroscope or infrared camera.

The positions of the through-hole fiducial 20 relative to the individualdetector elements or pixels 12 can be controlled with an accuracy ofapproximately 1 micron on the first side and a 2 micron on the secondside. Thus, the through-hole fiducial 20 gives an accurate indication ofthe location of the individual detector elements 12. This permits thedetector array 10 to be aligned relative to the surface by observing thelocations of the through-hole fiducial 20 since the positions of thepixels 12 relative to the fiducial 20 are known. The fiducial 20 may bealigned to a fixed reference formed upon the surface or to an opticalreference within the microscope.

Additionally, the through-hole fiducial 20 allow the positioning of thepixels 12 to be verified after mounting to signal processing modules.Improperly aligned arrays 10 can either be removed and re-aligned ordiscarded.

The through-hole fiducial 20 also provide a means for aligning signalprocessing modules having infrared detector arrays 10 mounted thereon.After the infrared detector arrays 10 are mounted to signal processingmodules, then the signal processing modules are assembled to form afocal plane array. This requires that the individual pixels 12 of eachdetector array 10 mounted upon a signal processing module be aligned tothe pixels of adjacent modules. This is easily accomplished by aligningthe fiducial 20 of the present invention. Alignment of signal processingmodules is discussed in further detail with respect to the thirdembodiment of the present invention and illustrated in FIG. 12.

The through-hole fiducials 20 may be formed by either etching or laserdrilling. Those skilled in the art will recognize that other methods arealso suitable. To etch the through-hole fiducials, their locations areincluded in the detector wafer implant mask. Thus, when the detectorwafer implant photoresists are formed, the features of the fiducial areincorporated. The fiducials may then be photolithographically developedduring wafer fabrication. They may then be either wet or dry etched toform small, i.e. 25 micron, cavities. These cavities can be furtheretched to form through-hole fiducials. If etching is preferred after thesupport substrate 22 is attached, then an etchant specific to thedetector material can be used such that the support substrate 22 isunaffected.

In the laser drilling method, the front side 16 of the array 10 islikewise etched by incorporating the location of the fiducial in thedetector Wafer implant mask. The etched fiducial are then used astargets for laser drilling and through-holes are formed.

Referring now to FIG. 5, a portion of a signal processing module 30 isdepicted. The signal processing module 30 has a plurality of electricalcontacts 32 formed upon one surface thereof. These contacts 32 arespaced on the same centers and correspond in number to the individualdetector elements 12. Thus the bump contacts 14 of the detector elements12 provide electrical connection between the infrared detector array 10and the signal processing module 30 when attached thereto.

Referring now to FIG. 6, two infrared detector arrays 40a and 40b andthe signal processing module 30 are depicted. Infrared detector array40a is shown aligned and attached to signal processing module 30.Infrared detector array 40b is shown aligned and in position to beattached to signal processing module 30.

To align the first infrared detector array 40a to the signal processingmodule 30, the bump contacts 14 of the array 40b are aligned to thecontacts 32 of the module 30. This assures proper positioning and goodelectrical contact. Fiducial 20a are used to visually align infrareddetector array 40a to signal processing module 30. This may beaccomplished by computing the position of the fiducial 20a of theinfrared detector array 40a relative to the individual pixels 12 formedthereon and then aligning the fiducial 20a to reference indicesrepresentative of the positions of the contacts 32 of the signalprocessing module 30. This may be easily accomplished by using acrosshair reference in an optical microscope or infrared camera system.For example, the crosshair may be placed at the position where aparticular fiducial is desired to be located and the infrared detectorarray 40a may then be positioned such that the fiducial 20a is alignedwith the crosshair. This process may be repeated for each of thefiducial 20a of the infrared detector array 40a. The desired positionsof the fiducial 20a may be easily calculated since the positions of thecontacts 32 of the signal processing module 30 are easily measured usingthe crosshair of the optical alignment system and the positions of thefiducial 20a relative to the individual pixels 12 are known.

Subsequent infrared detector arrays such as 40b must be aligned to thepixels 12 of any adjacent arrays as well as being aligned to theelectrical contacts 32. The fiducial 20b of the second infrared detectorarray 40b are similarly aligned to the fiducial 20a of the firstinfrared detector array 40a such that the pixels 12 of both arrays arealigned. This is easily accomplished since the positions of the fiducial20a and 20b are known relative to the pixels 12 of each infrareddetector array. Thus, the crosshair of the optical alignment system isplaced in the desired location of a particular fiducial 20b of infrareddetector array 40b and infrared detector 40b is manipulated into alocation such that the fiducial 20b is in alignment with the crosshair.This process is again repeated for at least two fiducials. Thus,alignment among pixels 12 of all infrared detector arrays attached to agiven signal processing module is obtained.

Alignment of adjacent signal processing modules 30 can likewise beachieved by aligning the fiducial of infrared detector arrays of onemodule to those of adjacent modules. Thus, a focal plane array can beconstructed wherein all pixels are in the desired alignment.

Referring now to FIGS. 7 and 8, a second preferred embodiment of themethod for aligning high density infrared arrays is depicted. In thesecond preferred embodiment of the present invention the back side 18 ofeach infrared detector array 10 is etched to form indicia which may beused for alignment purposes. Those skilled in the art will recognizethat various forms of indicia are suitable for alignment purposes. Forexample, a circle as depicted in FIG. 7 or a double square as depictedin FIG. 8 may be used.

The use of etched indicia upon the back side of infrared detector arrays10 avoids the need to etch or drill through-holes into the array 10. Theuse of etched indicia formed upon the back side 18 of each infrareddetector array 10 does however, require the use of a double side maskaligner and a separate mask for defining the locations of the etchedindicia.

Etched indicia such as those depicted in FIGS. 7 and 8 provideobservable reference points which may be used in the same manner as thethrough-hole fiducial described above. The fiducial or indicia 42 may beetched onto the back side of the infrared detector array 10 by placingthe array in a double side mask aligner, such as the Model MA25manufactured by Karl Suss. This is done prior to attaching the array tothe support substrate and preferably prior to dicing the wafer. It canalso be done after the substrate is attached so that fiducial is now onthe surface of the substrate.

A second mask containing the desired fiducial features is aligned to theprimary reference of the wafer located on the detector front side. Thispositions the mask, and consequently the fiducial to be formed, in aknown position relative to the pixels 12 formed upon the front of thearray 10. The back side of the wafer is then exposed and developed tolithographically imprint the fiducial features on the array back side.The wafer is then diced to form individual arrays. Thus, each individualarray may have a plurality of indicia or fiducial etched thereupon.

Referring now to FIGS. 9 and 10, double square indicia or fiducial 44are depicted as viewed through the transparent support substrate 22. Thedouble square indicia 44 are used in a manner similar to thethrough-hole indicia 20 of the first preferred embodiment of the presentinvention. The double square indicia 44 provide improved accuracy andease of use over both the through-hole indicia 20 and the circle indiciaof FIG. 7 in that the double square indicia 44 have straight edges whichmay be easily aligned with a crosshair. As shown in FIG. 8 the centerlines 34 and 36 may be easily aligned to an optical crosshair whereasthe center point of a circle indicia 42 of FIG. 7 or a through-holeindicia of the first embodiment require that the user visually estimatethe center of the circle or hole.

Referring now to FIG. 11, a third embodiment of the method for aligninghigh density infrared detector arrays of the present invention isdepicted. Notches 50 are formed along the edges 34 of the infrareddetector array 10. The notches are formed such that they areperpendicular to the upper 16 and lower 26 surfaces of the array. Thus,viewing a notch 50 from the back side 26 of the array 10 provides a trueindication of the location of the notch upon the front side 16 of thearray and thus provides a true indication of the pixel 12 positions.This is because the positions of the pixels 12 can be precisely measuredrelative to the notches 50.

This technique is suitable for both wafers and arrays that have alreadybeen diced from the wafer. The wafer or diced array is placed, frontside up, in a precision laser microprocessing machine such as Model 1000manufactured by XMR. A laser having a beam of approximately 10 micronsin diameter is used to scribe a plurality of notches 50 along the edgeportions of the array. If being performed upon a wafer, through-holesare formed where the wafer is to be diced such that after dicing notches50 are formed from the through-holes.

Nothing of the edge portions of the array has the added advantage thatthe notches 50 may be used as references during the stacking of anassembly of mosaic focal planes wherein each array is individuallyattached to a thin signal processing module and the modules aresubsequently stacked to form an array. In the stacking process the edgeportions of the individual photodetector arrays are visible and maytherefore serve as references.

Referring now to FIG. 12, three thin signal processing modules 46a, 46b,and 46c are depicted as they are being stacked to form a mosaic focalplane. Modules 46b and 46c are shown in alignment and module 46a ispositioned for attachment to module 46b. Infrared detector arrayassemblies 52a, 52b, and 52c are attached to modules 46a, 46b, and 46cprior to aligning modules 46a, 46b, and 46c. Thus, the notches 50 formedupon the assemblies 52a, 52b, and 52c may be used to align the modules46a, 46b, and 46c such that the pixels (not shown) formed upon eachinfrared detector array 10 will be aligned in the assembled mosaic focalplane array. As can be seen, alignment of the notches 50 of adjacentedges of assemblies 52a, 52b, and 52c results in alignment of theindividual infrared detector arrays 10. These notches 50 can be observedfrom various angles during the stacking process to facilitate alignment.For example, the notch formed upon the upper surface 54 of each assembly52a, 52b, and 52c can be observed by looking down at the assemblythrough an optical system. A crosshair within the optical system canthen be used to align successive grooves 50 to achieve the desiredpositioning.

It is understood that the exemplary method for aligning high densityinfrared detector arrays described herein and shown in the drawingsrepresents only presently preferred embodiments of the invention.Indeed, various modifications and additions may be made to suchembodiment without departing from the spirit and scope of the invention.For example, the precise shape and location of the through-hole fiducialof the first embodiment are not considered crucial to the presentinvention. It is only necessary that the position of the fiducial uponthe first surface of the array be known relative to the pixels and thatthe position of the fiducial upon the second surface of the array betrue to that upon the first surface. Also, various shapes and forms ofetched fiducial of the second embodiment of the present invention arecontemplated. Any shape which may readily serve as a reference point issuitable. Additionally, various means may be used to form thethrough-holes, notches, and indicia of the present invention. Thus,these and other modifications and additions may be obvious to thoseskilled in the art and may be implemented to adapt the present inventionfor use in a variety of different applications.

What is claimed is:
 1. A method for aligning an infrared detector arraywith an array of electrical connectors formed on a support surface, theinfrared detector array having first and second sides, and a pluralityof detector elements formed upon the first side thereof, the methodcomprising the steps of:(a) forming a plurality of indicia upon thesecond side of the infrared detector array, the indicia being disposedin predetermined positions in relation to the detector elements; (b)forming a corresponding plurality of reference indices upon the supportsurface proximate the array of electrical connectors such that theindices are disposed in predetermined positions in relation to theelectrical connectors; (c) attaching the second side of the infrareddetector array to a substrate, the substrate being transparent; and (d)positioning the first side of the detector array upon the supportsurface and aligning the indicia to the reference indices by observingthe indicia through the transparent substrate wherein alignment of theindicia and reference indices results in alignment of the detectorelements with the electrical connectors.
 2. The method as recited inclaim 1 wherein the step of forming a plurality of indicia comprisesforming apertures through the detector array, the apertures extendingfrom the first side of the array to the second side of the array.
 3. Themethod as recited in claim 2 further comprising the step of defining thelocations where apertures are to be formed by providing correspondingindicia on a detector pixel implant mask such that the locations aremarked on the first side of the array during the pixel implant process.4. The method as recited in claim 3 wherein the step of formingapertures through the detector array comprises etching apertures throughthe detector array at the locations marked on the first side of thearray.
 5. The method as recited in claim 4 wherein the step of etchingapertures through the detector array further comprises using an etchantspecific to the detector material such that the substrate is not etched.6. The method as recited in claim 3 wherein the step of formingapertures comprises the step of forming apertures through the detectorarray with a laser, the apertures being formed at the locations markedon the first side.
 7. The method as recited in claim 6 wherein the stepof forming apertures through the detector array with a laser comprisesforming apertures with a XeCl excimer laser.
 8. The method as recited inclaim 1 wherein the step of forming a plurality of indicia comprisesetching the indicia upon the second side of the detector array.
 9. Themethod as recited in claim 8 wherein the step of etching the indiciaupon the second side comprises:(a) placing the detector array in adouble side mask aligner; (b) aligning a mask for the second side of thedetector array to a primary reference located on the first side of thedetector array, said mask having the indicia formed thereon; and (c)exposing and developing the second side of the detector array to formthe indicia thereon.
 10. A method for aligning an infrared detectorarray with an array of electrical connectors formed on a supportsurface, the infrared detector array having first and second sides, anda plurality of detector elements formed upon the first side thereof, themethod comprising the steps of:(a) defining the locations whereapertures are to be formed by providing corresponding indicia on adetector pixel implant mask such that the locations are marked on thefirst side of the array during the pixel implant process; (b) formingapertures through the detector array with a laser, the aperturesextending from the first side of the array to the second side of thearray, the apertures being formed at locations marked on the first sideof the detector array, the apertures being disposed in predeterminedpositions in relation to the detector elements; (c) forming acorresponding plurality of reference indices upon the support surfaceproximate the array of electrical connectors such that the indices aredisposed in predetermined positions in relation to the electricalconnectors; (d) attaching the second side of the infrared detector arrayto a substrate, the substrate being transparent; and (e) positioning thefirst side of the detector array in laminar juxtaposition to the supportsurface and aligning the indicia to the reference indices by observingthe indicia through the transparent substrate wherein alignment of theindicia and reference indices results in alignment of the detectorelements with the electrical connectors.
 11. The method as recited inclaim 10 wherein the step of forming apertures through the detectorarray with a laser comprises forming apertures with a XeCl excimerlaser.